prefs: Use QWERTY (US) as the default custom layout

This layout definition contains some documentation and is a better
default than no text.

build.gradle

@@ -18,7 +18,7 @@ android {
     main {
       manifest.srcFile 'AndroidManifest.xml'
       java.srcDirs = ['srcs']
-      res.srcDirs = ['res']
+      res.srcDirs = ['res', 'build/generated-resources']
       assets.srcDirs = ['assets']
     }
   }
@@ -134,6 +134,7 @@ tasks.register('syncTranslations') {
 
 tasks.named("preBuild") {
   dependsOn += "initDebugKeystore"
+  dependsOn += "copyRawQwertyUS"
 }
 
 tasks.register('initDebugKeystore') {
@@ -145,3 +146,12 @@ tasks.register('initDebugKeystore') {
     }
   }
 }
+
+// latn_qwerty_us is used as a raw resource by the custom layout option.
+tasks.register('copyRawQwertyUS')
+{
+  copy {
+    from "res/xml/latn_qwerty_us.xml"
+    into "build/generated-resources/raw"
+  }
+}

srcs/juloo.keyboard2/LayoutsPreference.java

@@ -151,7 +151,7 @@ public void onClick(DialogInterface _dialog, int which)
               callback.select(new SystemLayout());
               break;
             case "custom":
-              select_custom(callback, "");
+              select_custom(callback, read_initial_custom_layout());
               break;
             default:
               callback.select(new NamedLayout(name));
@@ -203,6 +203,22 @@ void select(final SelectionCallback callback, Layout prev_layout)
       select(callback);
   }
 
+  /** The initial text for the custom layout entry box. The qwerty_us layout is
+      a good default and contains a bit of documentation. */
+  String read_initial_custom_layout()
+  {
+    try
+    {
+      Resources res = getContext().getResources();
+      byte[] raw = res.openRawResource(R.raw.latn_qwerty_us).readAllBytes();
+      return new String(raw, "UTF-8");
+    }
+    catch (Exception _e)
+    {
+      return "";
+    }
+  }
+
   class LayoutsAddButton extends AddButton
   {
     public LayoutsAddButton(Context ctx)